It was about 1950, and Ted Williams faced Nats ace Sid Hudson at Griffith Stadium. Hudson wound up, and just then the Nats catcher, a backup named Mickey Grasso, sang "You are my sunshine / my only sunshine / you make me happy / when skies are gray /you'll never know dear / how much I love you / please don't take / my sunshine / away", a popular song in the '40s.
The Splendid Splinter buckled over in laughter, and the umpire called "Strike one!"
Williams, trying to control a case of the giggles, turned to Grasso and said, "Mickey, don;t do that again".
Grasso replied, "Sure, Ted". He was quiet as Hudson wound up again, but, just as the Hudson let go, Mickey started up again: "You are my sunshine..."
Williams started to laugh again, but before Grasso got to "sunshine", Williams hit a line-drive over the center-field fence.
[Essence of story likely true. Heard it from my dad. Not sure if Hudson / Grasso were the battery.]